Britain's Queen Elizabeth, the world's oldest monarch, turns 90 next Thursday showing no sign she will be retiring from the stage anytime soon.

Her birthday comes months after she surpassed the 23,226 days her great-great-grandmother Queen Victoria spent on the throne to become Britain's longest-reigning monarch.

Since turning 65 in 1991, the nation has speculated about whether she would step aside in favor of her eldest son, Prince Charles. But aides and commentators say there is no prospect of her giving up her job.

"The queen has a phenomenal drive and energy and I think the fact that she still works is what keeps her going," Ingrid Seward, editor in chief of Majesty magazine, told Reuters.

"The queen doesn't want to put her feet up. This is what she wants to do, and this is what she's going to do for as long as she's fit and able to do so."

Born on April 21, 1926 in central London, Elizabeth still hosts state visits, presides over the annual state opening of parliament and holds a weekly audience with the prime minister.

While she has cut back on her once demanding schedule of foreign trips, those close to her say only incapacity would stop her from performing her royal duties. Last year she carried out 341 official engagements.

"As she turns 90, she's a remarkably energetic and guiding force for her family," her grandson Prince William said in a speech in India this week. "She maybe my grandmother, but she's also very much the boss."

Although Elizabeth's father died at the relatively young age of 56, her mother, who was known as Queen Elizabeth the Queen Mother, lived until 101 and was still appearing in public almost up until her death in 2002.

Her father only became king because her uncle Edward VIII abdicated to marry American divorcee Wallis Simpson.

Although monarchs in the Netherlands and Belgium have abdicated in recent years, there is no question that the queen will do so, royal historian Hugo Vickers told Reuters.

Others have suggested that one reason for the queen to hang on is the relative unpopularity of her son Charles, 66, already a record-holder as Britain's longest-serving heir apparent.

"When the queen's reign comes to its natural end, there is likely to be an urgent debate about the role of the royal family in modern Britain — a debate whose outcome is uncertain," royal author Anna Whitelock wrote in the Daily Mail newspaper.

"There is no absolute guarantee about the monarchy's long-term survival," Whitelock said.